In brief:
Acid, Suger, Neglect

Meth is caustic to all tissues, including the teeth, which can't repair themselves after damage like the rest of the body.

Meth users usually crave and consume lots of simple sugars which promote decay. They also neglect their entire body including their mouth. Put those three factors together and you have a perfect storm to destroy the teeth.

In brief:
Acid, Suger, Neglect

Meth is caustic to all tissues, including the teeth, which can't repair themselves after damage like the rest of the body.

Meth users usually crave and consume lots of simple sugars which promote decay. They also neglect their entire body including their mouth. Put those three factors together and you have a perfect storm to destroy the teeth.
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In brief:
Many reasons

Meth, like all "uppers" makes the body edgy and tight. The cost of prison dental care has exploded since meth became common. http://www.pbs.org/wgbh/pages/frontline/meth/body/.
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